The present invention relates generally to the joining of sheet metal or other sheet materials and more particularly to an apparatus for forming such joints, including leakproof and non-leakproof joints formed thereby.
It is old in the art to join a plurality of pieces of sheet metal by punching or otherwise manipulating them to cause them to be deformed into an interlocking relationship in a localized area. However, insofar as Applicant is aware, such joints typically require the shearing of the sheet material and hence are not suitable for leakproof applications unless a sealant is applied. The formation of such joints is also frequently destructive of the corrosion resistance of coated materials. In addition, the known apparatuses for forming the joints are frequently relatively complex in design, often requiring powered actuation of both a punch and one or more portions of the die, and frequently require expensive sliding die portions. This complexity increases the cost of the equipment, as well as the energy required for operation.
It has therefore been a primary object of the inventions of such above-mentioned applications and patents to provide an improved method and apparatus for permanently joining sheet metal or other sheet material items, with the capability of forming either leakproof joints or conventional "lanced" joints. Additional objects resided in the provision of forming apparatuses that included die members that were movable laterally, transverse to the longitudinal movement of a punch against an anvil between the dies. Such apparatuses were relatively simple but durable in construction, could utilize standard or specialized punches, required very little power, were compact and hence usable in many different applications, substantially preserved the corrosion resistance of coated sheet materials being joined, and were suited for use either as part of a small press or in C-frame holders in larger presses.
Another object of the inventions resided in the provision of improved die assemblies for use in sheet material joining apparatuses, and which were readily adapted to many different joint configurations, including conventional "lanced" joints as well as a novel leakproof joint formed by a radius-edged, non-shearing punch.
Further objects of the inventions of such patent applications and patents resided in the provision of novel leakproof joints for the sheet material as well as in the provision of novel methods for forming such joints.
Although these inventions performed well and were far superior to prior art apparatuses, the present application is directed to further, previously-disclosed aspects of these inventions, as well as to additional improvements and refinements thereon.
In accordance with the present invention, as defined in the appended claims, each of the preferred die members of the forming apparatus engage their adjacent die members in a substantially flush, no-gap relationship along laterally or radially-extending interfaces at least at the opening when the dies are in their closed positions. This feature provides for a more uniform and continuous periphery of the joints formed thereby, especially when the apparatus includes at least three of such die members, and preferably as many as six die members, or even more. This feature distinguishes the invention from prior collet-type die apparatuses, as well as from other types of forming apparatuses wherein the multiple die members are formed from a single piece of stock that is cut laterally to separate individual die members.
Furthermore, as is discussed in more detail below, the provision of larger numbers of die members or die segments contributes greatly to the stability of the forming apparatus by minimizing the tendency for any of the die members to become detached and separated from the die assembly or forming apparatus. This is the case especially in apparatuses for forming round joints, because each of the larger number of die members is required to move a shorter lateral distance away from the anvil during the forming of the interlocked joint than is the case with fewer numbers of die members, thus minimizing the tendency of any of the die members to be detached from the retention structure that holds the dies in place against the longitudinal advances and withdrawals of the punch.
The die assemblies according to the present invention can also be shorter (in the longitudinal direction), and thus more compact and useable in cramped applications where space is at a premium. In such applications, the moving parts of the die assembly (not including the punch) reside within an envelope having a longitudinal dimension no greater than the lateral dimension of the closed die opening into which the sheet material is then forcibly drawn by the punch during forming of the joint. This compact feature, which has previously not been practical (or even possible in previous designs, such as those using resilient collet-type die assemblies) greatly enhances the widespread applicability of the present invention.
The present invention also includes a stripper, or sheet material retainer, member that preferably has an outside diameter (or outer lateral dimension) at the area of longitudinal engagement with the sheet material to be formed that is greater than the inside diameter of the die opening when the dies are at their maximum laterally-outward open positions. This, coupled with strong forces urging the stripper/retainer longitudinally against the sheet material surrounding the joint in order to clamp the sheet material pieces together, greatly reduces (or substantially eliminates) the tendency for the joint material to flow longitudinally outward, away from the preferably-fixed anvil inside the die opening.
These features, along with others discussed in more detail below, yield die assemblies and forming apparatuses that are more durable and reliable, more versatile, more stable, more widely applicable (especially in cramped spaces), and that typically require less maintenance and less energy to operate than previous apparatuses.
These and other objects, features and advantages of the present invention will become apparent from the subsequent description and the appended claims, taken in conjunction with the accompanying drawings.